import React, { Component } from 'react'

export default class Count extends Component {
  state = { count: 0 }
  increment = () => {
      const {value} = this.selectNumber;
      const {count} = this.state;
      this.setState({count: count+Number(value)})
  }
  decrement = () => {
    const {value} = this.selectNumber;
    const {count} = this.state;
    this.setState({count: count-Number(value)})
  }
  // 奇数再加
  incrementIfOdd = () => {
    const {value} = this.selectNumber;
    const {count} = this.state;
    if(count % 2 !== 0) {
        this.setState({count: count+Number(value)})
    }
  }
  incrementAsync = () => {
    const {value} = this.selectNumber;
    const {count} = this.state;
    setTimeout(() => {
        this.setState({count: count+Number(value)})
    }, 500);
  }
  render() {
    return (
      <>
        <h1>当前求和为: {this.state.count}</h1>
        <select ref={(c) => (this.selectNumber = c)}>
          <option value="1">1</option>
          <option value="2">2</option>
          <option value="3">3</option>
        </select>
        &nbsp;
        <button onClick={this.increment}>+</button>&nbsp;
        <button onClick={this.decrement}>-</button>&nbsp;
        <button onClick={this.incrementIfOdd}>当前求和为奇数再加</button>&nbsp;
        <button onClick={this.incrementAsync}>异步加</button>&nbsp;
      </>
    )
  }
}
